1. Field of Invention
This invention relates to a cryosurgical instrument suitable for use in destroying living tissues, such as solid malignant or benign tumors. More particularly, the invention relates to a surgical system including one or more cryoprobe instruments capable of producing very low temperatures and which is highly effective in the surgical treatment of various disorders, especially for destroying tumors. Even more specifically, the invention relates to a surgical system, including at least one cryoprobe, with means for producing at the probe tip temperatures below the freezing temperature of tissue (-0.57.degree. C.), using liquid nitrogen as the coolant, which coolant temperatures can be lower than the normal boiling temperature of nitrogen. The invention also relates to cryoprobe instruments which have variable controlled active cooling region (freezing zone) as well as cryoprobe instruments and connecting lines with active vacuum thermal insulation, as well as to a cryosurgical operating method in which the surgeon may adjust the freezing zone length in one or more cryoprobe instruments in response to images taken of the tumor prior to or during cryosurgery.
2. Discussion of Prior Art
Cryosurgery is a surgical procedure that uses freezing temperatures to destroy tissue. James Arnott, an English physician, was the first to introduce this method in 1865 for treatment of cancer of the skin. Between 1920 and 1940, the commercialization of liquid air led a number of surgeons to employ freezing to accomplish the destruction of nondesirable tissue. By 1930 the first monograph on the method was published (Lortat-Jacobs and Solente, 1930).
Modern cryosurgery started with the work of a New York surgeon, I. Cooper, who in 1961 developed a new apparatus for cryosurgery. This apparatus consisted of a hollow metal tube which was vacuum insulated, except at the tip, through which liquid nitrogen was circulated. Cooper was able to localize the freezing and, thereby, treat the tissue in a controlled way. The method was used first for treatment of Parkinsonism, and later extended to tile destruction of nondesirable tissue in other areas, such as dermatology, proctology, gynecology. The applications of cryosurgery are numerous and have been described in several texts and review papers, (Rand, et al., 1968; Albin 1980; Gage 1982; Zacarian, 1985; Gage, "Cryosurgery For Cancer", Compr. Ther. January 1984; 10(1):61-69; Gage and Torre, 1988; Onik and Rubinsky, 1988).
Until recently, cryosurgery has been applied primarily to treatment of tumors on the outer surface of the body, such as for treatment of skin cancer. Despite the remarkable rate of success with treatment of tumors on the outer surface of the body by cryosurgery (97% survival with treatment of cancer of the skin by cryosurgery, Gage 1982), and despite evidence that cryosurgery may be as efficient deep in the body, (Onik and Rubinsky 1989), the cryosurgery technique is not applied, at this stage, extensively to treatment of nondesirable tissue deep in the body.
Some major problems that hindered the efficient application of cryosurgery to the treatment of cancer and other nondesirable tissue, were that, for example, it had been impossible to observe the extent of the frozen region during cryosurgery, and there was no good understanding of the mechanism by which tissue is destroyed during freezing. Consequently, cryosurgery was typically used for treatment of disease in easily accessible areas, e.g. skin, eyes, nose, where the extent of the frozen tissue could be observed visually.
The prior art devices are, in general, of either of two types, the spray type, wherein the cold refrigerant is sprayed directly onto the tissue to be destroyed, or the closed end cryotip type, in which the refrigerant is delivered to a portion of the tip that is inserted in the tissue to be necrosed. Apparatus described in U.S. Pat. No. 4,376,376 issued to Gregory is exemplary of the spray type devices. The device described in U.S. Pat. No. 4,211,231 includes interchangeable spray and closed end cryotips. Other representative patents disclosing closed end cryotip devices include, for example, U.S. Pat. Nos. 3,971,383 - van Gerven; 4,202,336 - van Gerven; 3,782,386 - Barger, et al.; 3,398,738 - Lamb, et al.; 4,015,606 - Mitchiner, et al.; 3,859,986 - Okada, et al.; 4,831,846 - Sungaila. Typical to these prior art devices, which were developed in response to the known science prior to the recent developments of Onik and Rubinsky, is the fact that the extent of the freezing region was not controlled accurately because there was no way to observe the dimension of the tumor and of the tumors deep in the body. Therefore, an accurate control would not have been useful in any event. While the prior art systems were designed to achieve the lowest possible temperature on the closed end tip, as fast as possible, to ensure that as much of the closed end tip (hereinafter often referred to as "freezing zone") as possible reaches as low a temperature as possible, there were, nevertheless, often substantial differences between the temperature of the refrigerant and the temperature of time freezing zone probe tip.
Two major new advances were made recently in the area of cryosurgery. They are reviewed in the paper by Rubinsky and Pegg, Proc., R. Soc. Lond. B234, 343-358 (1988). It was found that monitoring by imaging techniques, such as magnetic resonance imaging or ultrasound, can be used intraoperatively to determine, in real time, the extent of the tumors, as well as that of the frozen tissue during cryosurgery. Ultrasound works by sensing a pressure wave from a pressure transducer. The wave is reflected from boundaries between regions that have differences in acoustic impedance such as between tumors and normal tissue, blood vessels and tissue and frozen and unfrozen tissue. The reflected wave is identified by tile pressure transducer and the extent of the tumor, or of the frozen region, is shown on a monitor. Following computerized interpretation of the data, this procedure facilitates an accurate identification of the extent of the tumor and of the frozen region during cryosurgery. Also, recent experiments described in the previously mentioned article by Rubinsky and Pegg, have shed new light on the process of freezing in tissue. The results show that freezing in tissue is strongly affected by the structure of the tissue. Rather, it was shown that ice forms first in the blood vessels, while tile cells surrounding the frozen blood vessels remain unfrozen. The rejection of saline during the freezing of the blood vessels causes an increase in the saline concentration in the solution inside the blood vessels. This causes water to leave the unfrozen cells through the cell membrane into the blood vessel. The consequent expansion of the blood vessels leads to the destruction of the vessels. Apparently the destruction of the frozen tissue is promoted by the fact that during freezing the vasculature network is destroyed and, therefore, cancerous and other nondesirable cells in the region that has been frozen are deprived of their blood supply after thawing and die because of ischemic necrosis. It was shown in the same paper that tissue can be destroyed by freezing to temperatures as high as -2.degree. C. Furthermore, it was also shown that this mode of destruction is pronounced at the outer edge of the frozen region. This implies that the image seen on the ultrasound also corresponds to the extent of the frozen region. The work of Rubinsky, et al. also shows that destruction of the vasculature network can be optimized by varying the temperature of the cryosurgical tip in a predetermined controlled way.
The commonly assigned U.S. Pat. No. 4,946,460 of Merry and Smidebush, the disclosure of which is incorporated herein in its entirety by reference thereto, provides a cryosurgical system and method which incorporate these new discoveries by including control means for precisely controlling the heating and cooling of the cryosurgical probe in accordance with a desired temperature regimen.
While good results can be obtained by operating a cryosurgical probe instrument according to predetermined temperature-time profiles, there still remain several problems to be solved before cryosurgical procedures and cryosurgical devices become more readily available to the art.
For example, the new ability to observe, with ultrasound, prior to surgery the extent of the tumor and during surgery the extent of the frozen tissue have raised additional demands from cryosurgical probes that cannot be readily achieved with the available devices. In the past, when the extent of the tumor or of the frozen tissue were not known accurately, the surgeons could not demand that the extent of the frozen region accurately correspond to the tumor. Therefore, prior devices did not have to provide a well specified frozen region to fit the particular tumor that was treated and, in fact, it was impossible to control the performance of prior devices and to determine whether it freezes according to the desire of the surgeon. All that was known was the fact that the temperature at the tip of the cryosurgical probe drops and a certain amount of freezing occurs. Since the surgeons were unable to determine how much freezing occurs, there was no method to determine if the existing devices performed satisfactory or not, neither was there any specific desire to develop devices that can accurately freeze predetermined domains. However, with the clinical application of ultrasound monitoring to cryosurgery, the flaws of the existing devices with respect to the ability to freeze accurately unhealthy, e.g. cancerous, tissue have become evident. The major flaws of the existing devices for clinical practice are related to the minimal temperature that they can achieve and, therefore, to the actual extent of the tissue which they can freeze, and to the extent the actively freezing part of the tip, which in most of the devices is predetermined and, therefore, there is no flexibility in adjusting the extent of the freezing region to the size of the tumor. The new device and system described herein were developed in response to these problems. Furthermore, because of the relative small number of cryosurgeries made in the past, past design requirement for the probes in terms of their ability to handle numerous surgeries were not as stringent as those which the inventors started facing with the increase in the appeal of this procedure and in the number of surgeries performed. Therefore, one of the features of the invention probes is their ability to withstand the rigors of increased use.
It is still often necessary and desirable to be able to achieve probe tip freezing zone temperatures lower than -196.degree. C., tile normal boiling point of liquid nitrogen. Lower temperatures can provide higher efficiency in tissue destruction by freezing larger areas with the same probe tip size and geometry, i.e. surface area, or alternatively, the same freezing area with smaller probe tip diameter or surface area.
Most conventional cryosurgical probe instruments operate with liquid nitrogen (LN.sub.2) or other liquefied gas as the cooling medium. The LN.sub.2 is introduced into the freezing zone of the probe through a feed or delivery tube (which is usually the innermost tube of three concentric tubes). The delivery tube extends into an expansion chamber at the closed probe tip end but terminates a distance from the tip. The LN.sub.2 immediately and rapidly vaporizes and undergoes over a one hundred-fold increase in volume. As the liquid vaporizes or gasifies, it absorbs heat from the probe tip to lower its temperature, theoretically to the normal boiling point of LN.sub.2 (about -196.degree. C.). However, in actual practice, as time liquid nitrogen boils a thin layer of nitrogen gas [N.sub.2 (g)] inevitably forms on the inner surface of the closed probe tip end. This gas layer which has a high thermal resistance acts to insulate the probe tip freezing zone such that the outside probe tip temperature does not usually fall below about -160.degree. C. This effect is known as the Liedenfrost effect. Additional inefficiencies result when the back pressures produced by the boiling LN.sub.2 reduce the LN.sub.2 flow into the freezing zone, thereby further reducing the efficiency of the probe tip to cool. Another problem posed by prior art systems is that the "cold" N.sub.2 (g) is simply vented directly to the atmosphere because there is no effective or economical way to recover it. The "cold" vented N.sub.2 (g) is not only wasted but produces a cloud of condensate upon exposure to atmospheric moisture in the operating room. While not particularly harmful, it can be unsightly and disconcerting.
Accordingly, one object of this invention is to provide a cryosurgical probe device which can generate probe tip freezing zone temperatures at least as low as the normal boiling temperature of nitrogen.
Another object is to provide a cryosurgical probe device wherein cooling can be effected when desired with a cooling liquid maintained at such temperatures and pressures which avoid or minimize boiling or vaporization of the liquid coolant.
Still another object is to provide a cryosurgical probe device and system which avoids or minimizes venting of "cold" gasified coolant directly to the atmosphere.
Another and related object is to provide a cryosurgical probe instrument and system in which liquid nitrogen refrigerant is recovered after exiting from the cryoprobe and is available for recooling and recirculation.
In order to maintain the low temperatures of the liquid cryogenic refrigerant as the cooling medium flows through the cryoprobe device and also to avoid subfreezing and tissue damaging temperatures on the walls of the cryoprobe device other than the freezing zone of the probe tip almost all known cryoprobe devices will include insulation inside the cryoprobe and surrounding the coolant delivery and return or exit lines downstream of the freezing zone. Most typically the insulation of the probe tip is provided in whole or in part by a permanent or static vacuum downstream of the freezing zone portion of the probe tip which vacuum will also thermally isolate the freezing zone end of the probe tip from the downstream end of the probe tip. For this purpose, the freezing zone and expansion chamber of the probe tip is separated from the downstream end of the probe tip by some form of seal.
However, the requirement for a permanent vacuum substantially increases tile cost of the cryoprobe device since it entails very high precision machining and welding of the vacuum seals. For example, the coolant delivery and return tubes need to extend through the seal to communicate with the closed probe tip end and precise machining and welding of these tubes to apertures in the seal and to the probe shell or casing is required. Furthermore, because the cryoprobe device necessarily undergoes cycles of expansion and contraction as the device goes through cooling and heating cycles even the best formed vacuum seals tend to form leaks requiring the entire device to be discarded. At a minimum, this entails very considerable expense, but if the leak occurs during surgery, even more severe problems will obviously arise.
Conventional cryosurgical probes generally have the probe tip permanently affixed to a probe instrument body, including a handle member, for example. See, however, e.g. the aforementioned U.S. Pat. No. 4,211,231, for removable and interchangeable probe tips. In the surgical destruction of tumors by freezing, different size probe tips may be required to treat different sizes and shapes of tumors. However, it is not generally practical or feasible to design or have available probe tips which have the ideal or optimum freezing area/length for every conceivable type of tumor. Therefore, there have been some proposals in the prior art to provide cryosurgical probe devices with means for adjusting the freezing zone by manipulating the length or penetration of the coolant delivery and/or coolant line with respect to the expansion chamber of the probe tip. For example, Lamb, et al. in U.S. Pat. No. 3,398,738, provides a cryosurgical probe in which the liquid refrigerant delivery tube may be longitudinally or axially adjustable with respect to the probe housing. However, the mechanism for making the adjustment is rather complicated. U.S. Pat. No. 4,015,606 to Mitchiner, et al. discloses a cryosurgical probe having a cooling chamber that is permanently separated from the insulating chamber in which a supply conduit extends into the cooling chamber of the probe tip, wherein the freeze zone in the cooling chamber is controlled by adjusting the position of the refrigerant exhaust conduit in the tip relative to the position of the supply conduit. However, only minor, if any, adjustment is available with this device. Furthermore, the problems inherent in permanent vacuum seals still exist.
Accordingly, another object of this invention is to provide a cryoprobe surgical instrument which is comparatively easy and inexpensive to manufacture.
It is another object of the invention to provide a highly efficient cryoprobe surgical instrument which is made from relatively inexpensive parts and construction and which is intended for only a single or few uses and can then be discarded.
A related object is to provide a cryoprobe surgical instrument which does not require a permanent vacuum or high precision meals to thermally isolate the probe body from the probe tip or to insulate the coolant delivery and return lines or tubes from the outside walls of the probe tip other than in the freezing zone at the closed end of the probe tip.
A still further and related object is to provide a cryosurgical probe device and system which includes means for continuously withdrawing gas from the probe tip behind the active freezing zone at the closed end of the probe tip, as well as in the conduits supplying the cryogenic liquid refrigerant to the probe tip, to form and maintain an active or dynamic vacuum to thermally insulate the probe tip and the refrigerant supply lines from the source of the cryogenic coolant to the probe tip.
It is still another object of the invention to provide a cryosurgical probe instrument with a seal which is not permanently fixed to the outer shell or casing of the probe tip but which in operation effectively separates the freezing zone of the probe tip from the remainder of the probe tip, i.e. downstream, with respect to the inflow of coolant liquid, of the seal.
Another object of the present invention is to provide a cryosurgical probe laving a simplified but effective means for adjusting the freezing zone of the probe tip by changing the region of insulation relative to the closed end of the probe tip, thereby allowing prior determination of the freezing zone region and thus facilitating the controlled application of cryosurgery to only the regions in which the surgeon determines to freeze the tissue.
Another drawback to conventional cryosurgical instruments is that quite often a tumor is too large or irregularly shaped to be totally destroyed with only a single probe tip and, notwithstanding the use of ultrasonics or other techniques for "observing" tile tumor prior to surgery, it often happens that the size and shape of the tumor is not fully recognized until after surgery begins. Also, it is not uncommon for a surgeon to find multiple tumors during surgery. With only a single cryosurgical instrument probe, the surgeon cannot always efficiently or safely treat large, or a larger than expected tumor or multiple tumors. If several cryoprobes are available, it may still be difficult to simultaneously connect more than one probe to the liquid nitrogen source. On the other hand, if a system for connecting multiple probes to the cryogenic refrigerant supply is available, it Would still be necessary to have a simple, reliable and safe means for determining which of tile several available probes was receiving coolant, which probe tips were at the desired low temperature or sufficiently warmed for being safely removed. It would also be advantageous to be able to individually control the cooling and heating rates of multiple probes and probe tips.
Therefore, it is still another object of the invention to provide a cryosurgical system capable of effectively and safely destroying one or more tumors of varying sizes and shapes using a multiplicity of cryosurgical probes the probe tip temperatures of which can be individually controlled by the surgeon or surgical team member during surgery.
Still yet another object of the invention is to provide a cryosurgical system in which all components required for effectively performing a cryosurgical procedure, including vacuum pump, liquid nitrogen supply, multiple cryosurgical probes, hoses, tubes and other connecting lines, control apparatus and sub-cooling refrigeration system, are contained within a compact movable unit and, all components can be easily and quickly set-up for convenient access by the surgeon and surgical team.